Biological and Electrochemical Treatment of Used Metalworking Fluids: A Toxicity-Reduction Evaluation

Abstract

The aim of this study was to evaluate and compare the toxicity of spent metalworking fluids (MWFs) and two different effluents obtained by biologic and electrochemical treatment of spent MWFs toward aquatic organisms of different trophic levels. The obtained toxicity data was used to calculate safe concentrations of both effluents. The spent MWFs without treatment showed the highest toxicity among the tested samples and should be classified as "extremely toxic" (toward invertebrates) or "very toxic" (toward other test organisms). Both methods applied for MWFs treatment resulted in a significant decrease in toxicity of the treated MWFs, but the obtained effluents had still to be regarded as "toxic". The ranges of the values of acute toxic units for both effluents were significantly narrower than for the untreated spent MWFs. The values of the safe concentrations of the spent MWFs, the biologic effluent, and the water phase resulting from electrochemical emulsion breaking were equal to 0.013%, l.8%, and 1.3%, respectively, corresponding to chemical oxygen demand concentrations of 1.8%, 32, and 34 mg O(2)*L(-1). These values are far lower than the discharging limit of 125 mg O(2)*L(-1) for industrial effluents, according to the relevant Polish regulations. It is therefore recommended to include toxicity bioassay parameters into guidelines for wastewater discharges to surface waters because the existing chemical and physical parameters are not sufficient to describe the environmental impact of industrial wastewater. Toxicity bioassays can be a promising tool for evaluating the efficacy of unit operations in industrial wastewater treatment (toxicity reduction evaluation) as well as identification of toxic substances in effluents (toxicity identification evaluation).

Bioremediation Of A Spent Metalworking Fluid With Auto- And Allochthonous Bacterial Consortia

“…Microbiologically-based treatment processes make use of the activities of activated sludges working in aeration chambers of wastewater treatment plants or of bacterial consortia constructed upon specialized strains [9,22,34,35,39,40,42]. Bioremediation of recalcitrant MWF constituents was shown to be effective either with aerobic or anaerobic methods [9,14,39,49].…”

“…Although these teams dealt with a similar subject their methodologies involved different approaches such as a long-term simulated wastewater flow setup [39], mixed anoxic/aerobic SBR cycles [35], combined two-step anaerobic/aerobic process [39], hybrid physical-biological or chemical-biological treatments [34,41] or high dilution of the MWF wastewater (concentrations below 3%) [42]. Moreover, it has to be emphasized that different working-fluid sources generate effluents varying dramatically in their chemical content.…”

“…For that reason microbiological remediation has been proposed as an advantageous and high-yield method, which may serve as a cost-competitive, low energy demanding and environment-friendly alternative [10,11,[32][33][34][35][36][37]. The applicability of biological methods is particularly high for the treatment of water-miscible emulsions.…”

“…The first strategy involves either biostimulation of the indigenous microflora within the treated MWF [9,39] or selection of the most active strains from various MWF samples, then cultivation and inoculation to a new wastewater to be treated [9,30,34,35,[40][41][42]. The use of indigenous microorganisms is of a special interest since their resistance to a complex chemical content of MWFs might result in elevated xenobiotic biodegradation activity [13,14,40,43].…”

Treatment of automotive industry wastewater using anaerobic batch reactors: The influence of substrate/inoculum and molasses/wastewater

“…These liquids enable the removal of swarf and metal parts. The global use of MWF is estimated at more than two million cubic meters (Muszyn'ski et al, 2007). Some 97% of the energy used in metal working operations is converted to heat, which can cause cutting tools to loose rigidity and make it difficult to produce workpieces within desired tolerances.…”